Pneumatic impact tool

ABSTRACT

The impact tool disclosed includes a housing, an anvil in the lower end of the housing, and a hammer to reciprocate in the housing and strike the anvil a series of blows. A stationary hollow valve member extends into an opening in the top of the hammer and supplies air under pressure from the pipe string to passageways in the hammer that conduct the fluid alternately to opposite ends of the hammer to cause the hammer to reciprocate in the housing. The arrangement is such that the actuating air acts across the entire cross-sectional area of the upper end of the hammer during its power stroke. Also, a hollow stationary bottom valve can be used to control exhaust from the tool and arranged so that the actuating air acts against the entire cross-sectional area of the hammer during its return stroke.

United States Patent 1191 Bassinger PNEUMATIC IMPACT TOOL [75] Inventor: Ross Bassinger, San Antonio, Tex.

[73] Assignee: Reed Tool Company, Houston, Tex.

[22] Filed: June 19, 1972 [21] Appl. No.: 264,019

Related US. Application Data [63] Continuation-in-part of Ser. No. 116,980, Feb. 19,

1971, abandoned.

[52] US. Cl 173/73, 173/17, 173/66 [51] Int. Cl. E2lb 5/00, E21c 7/00 [58] Field of Search 173/64, 73, 77, 80, 132, 173/136, 138; 91/234 {56] References Cited UNITED STATES PATENTS 711.859 10/1902 Holden 173/136 X 727,954 5/1903 ller 173/136 1.518.124 12/1924 Mcrccr 173/138 1,601,733 10/1926 Gilman 173/105 1,726,352 4/1927 Hulshizer ..'....91/234x Primary ExaminerHenry C. Sutherland Assistant Examiner--William F. Pate, lll

[ 5 7] ABSTRACT The impact tool disclosed includes a housing, an anvil in the lower end of the housing, and a hammer to reciprocate in the housing and strike the anvil a series of blows. A stationary hollow valve member extends into an opening in the top of the hammer and supplies air under pressure from the pipe string to passageways in the hammer that conduct the fluid alternately to opposite ends of the hammer to cause the hammer to reciprocate in the housing. The arrangement is such that the actuating air acts across the entire cross-sectional area of the upper end of the hammer during its power stroke. Also, a hollow stationary bottom valve can be used to control exhaust from the tool and arranged so that the actuating air acts against the entire crosssectional area of the hammer during its return stroke. 11 Claims, 13 Drawing Figures Qu t PAIENIED 3.826.316

sum 5 or 5 //2 I I Q PNEUMATIC IMPACT TOOL This application is a continuation-in-part of my copending application Ser. No. 116,980, filed Feb. 19, 1971, now abandoned.

This invention relates to impact tools that are powered by air pressure.

Impact tools of the type to which this invention relates have a hammer that reciprocates in a housing and beats on an anvil located in the path of the hammer. The hammer is reciprocated by a gas under pressure, usually compressed air, that acts alternately against opposite ends of the hammer. The energy transmitted to the anvil by the hammer is transmitted by the anvil to a drill bit.

Many air actuated impact tools are operated at speeds ranging from several hundred to several thousand cycles per minute, For this reason, it is desirable that they have as few moving parts as possible. In particular, poppet type valves are undesirable, not only because they have the'movement of a valve element into and out of engagement with a seat, but because they usually have springs that will fatigue and fail.

Another design aspect of impact tools is the location of the passageways that conduct the air to chambers where the air can exert a force against the hammer and cause it to move. When these passageways are located in the walls of the housing in which the hammer reciprocates, they not only weaken the walls, but they complicate the construction of the housing. This makes the tool more expensive to build.

Preferably, then, an impact too] should have only one moving part, the hammer itself, and be designed so at least most of its air passageways are located in the hammer and can be formed by a simple drilling or milling operation. It is an object of this invention to provide such a tool.

It is another object to provide such an impact tool having an improved arrangement of valves and gas passageways to alternately direct actuating gas to and away from the ends of the hammer.

It is another object to provide such an impact tool in which the hammer is the only moving part and in which an area equivalent to the full cross-sectional area ofthe hammer can be acted on by the air when the hammer is being moved toward the anvil, i.e., during the power stroke of the hammer.

It is another object to provide a pneumatic impact tool wherein the air that acts against the upper end of the hammer during the power stroke acts against an area which is limited only by the inside diameter of the housing so that the maximum downward force can be obtained to urge the hammer downwardly for a given size tool and air of agiven pressure.

Another object is to provide such an impact tool wherein the actuating air acts against the entire crosssectional area of the hammer during its push-up stroke.

These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a considerationof this specification including the attached drawings and appended claims.

In the drawings:

FIGS. 1A and 1B are vertical cross-sectional views through the preferred embodiment of the impact tool of this invention showing the hammer at the end of its downward or power stroke;

'FIGS. 2A and 2B are sectional views similar to the views of FIGS. 1A and 18 with the hammer at the upper end of its stroke just before the beginning of the power stroke;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1A;

FIG. 4 is a cross-sectional view taken along line 44 of FIG. 2A;

FIG. 5 is a vertical cross-sectional view of another embodiment of this invention;

' FIG. 6 is a view similar to'FIG. 5 except that the hammer is shown in another of its positions; 7

FIG. 7 is an enlarged view of the central portion of FIG. 5;

FIGS. 8, 9 and 10 are views taken on the lines 8+8, 9-9, and10-10 of FIG. 7;

FIG. 11 is a view similar to FIG. 7 except'that the parts are shown with the tool suspended as from a drill string; and

FIG. 12 is an enlarged vertical cross-sectional view of a check valve which can be used as a part of the tool when desired.

The impact tool shown includes atubular housing that is adapted to be connected into astring of drill pipe. In the embodiment shown, the housing has a tubular portion 10 connected to an upper sub '12, which provides a connection for the housing to drill string 13,

only the lower portion of which is shownin the draw- Anvil means are provided to be struck by a hammer and to transmit the impact of the hammer to a drill bit or'other working tool. In the embodiment shown, anvil 14 is located in the lower end of housing portion 10. It includes shank portion 14a and threaded box portion 14b for connecting the anvil to drill bit 15, only the upper portion of which is shown. Shank 14a has external groove 16 in which split ring 17 is locatedJLower sub 18 is connected at the lower end of housing portion 10 to engage ring 17 and pick up the anvil and bit and support them asthe tool is being run in the hole. When the bit engages the bottom of the hole, it will stop and the housing can be lowered into engagement with the shoulder of box 14b, as shown in FIG. 1B. In this way, the drill string can apply a downward force to the bit while the impact of the hammer on the anvil is transmitted directly to the-bit and not to the housing of the tool or the drill string. Also, as will be explained in more detail later, such a sliding connection between the anvil and the housing causes the tool to become inoperative, when the bit is off the bottom of the well bore and the bit and anvil are hanging from ring 17.

Skirt 19 is connected to sub 18 and extends downwardly over a portion of box 14b of the anvil to keep the space between the box of the anvil and the lower end of member 18 from getting filled with cuttings, sand, or the like when the tool is being run into the hole, which could prevent the desired telescoping of,

the anvil relative to the housing. A driving connection tivelyr Hammer 20 is locatedin housing portion to reciprocate therein and strike the upper end of anvil 14 at the end of its power stroke. The anvil has an upwardly facing surface or anvil face 21 that stops the downward travel ofhammer- 20 and receives the impact of the hammer when it reaches the end of its downward travel. j

A first or lower chamber designated A is located in the housing between lower end surface 20a of hammer 20 and anvil face 21. In the embodiment shown, sleeve valve 22 .is located in the upper end of opening 23 that extends throughthe anvil. Sleeve valve 22 has upwardly extending portion 22a that extends into opening 24in the lower end of hammer when the hammer is in engagement with the anvil. Thus, chamber A is opened to the exterior of the tool when the hammer has moved through at least a portion of its-returnstroke and closed when sleeve portion 220 extends into opening 24. The external diameter of sleeve portion22a is such that when the sleeve is in opening 24, the flow of air from the chamber defined by the sleeve, the lower 1 end surface of the hammer, the anvil face, and housing portion 10 will be restricted sufficiently for the air to buildupsufficient pressure in thecham-ber to move hammer 20 upwardly in its-return stroke so that it can begin another power stroke afterthe'chamber has been exhausted/The length of the'sleeve above the anvil determinesithe push-up stroke of the hammer, i.e., dis tanceof the a'irpressure inthechamber will act topush the hammerupwa rd before the chamber is opened to exhaust. Thisin turn is dependent on the weight of the hammer, the stroke and frequency of the hammer, and the air pressure available. However, the hammer will usuallycontinue itsupwa'r d travel after the chamber A is exhausted and this can be termed over-travel.

A second chamber designated B is located in the housing above the upper end of the hammer.- The chamberis defined by housing closingmember or' sub 12, housingportion .10, the hammer itself, and elongated hollow member 26. Elongated hollow member 26 is locatedin opening 33 of sub 12. It has flange 28 that restson shoulder'29 formed by reducing the diameter of opening 33. It is held in such position by sleeve 30 and snap ring 31. This arrangement places bore 32 of the hollow member in fluid communication with bore 33 of closing member or sub 12, which in turn is supplied with air from drill pipe 13.

Tubular valve member 26 extends below sub or closing memberlZ into a counterbore or blind hole 35 in hammer 20. Thusethe valve member is positioned to telescope with aportion of the hammer and, as shown,

has a slidingfitfin the counterbore. Hollow member 26 is a stationary valve member that isfixedrelative to the housing and which is located in the center of the housing. The valve member is provided with outlet port a means comprising, in the embodiment shown, two longitudinally spaced series of openings 36 and 37, respec- Passageway means are provided to alternately connect the outlet port means of the stationary valve member to first (lower) and second (upper) chambers A and B, respectively, to cause the hammer to recipro to a-minimum; Sections taken along a single plane would show passageways on one side of the longitudinal axis that are a mirror image of thepassageways on the other side as indicated in FIG. 3. I

I The two lateral passageways 38 are intersectedf'by verticalpassageways-39a and 39b (FIG. 3) which extend downwardly through hammer 20 to the lower-en thereof where they open into first chamber A. V

. Passageway means are also provided toconduct air from the'outlet meansof hollow member 26 tosecond chamber B, when the hammeris a predetermined distancefrom housing closing member 12. In the embodiment shown, blind opening 35 in the upper end of hammer 20 has a second section 40 of increased diameter into which air can flow when this section of opening 35 moves to a position opposite opening 36. From enlarged diameter section 40, the airflows laterally through passageways 41a and 4112, as shown in FIG. 4, v

to longitudinally extending grooves 420 and 42b in the sides of hammer 20. These grooves combine with housing' 10 to provide vertical passageways through which theaircan flow into second chamber B to act over the annular cross-sectional area of the upper end of the hammer and drive .the hammer downwardly in its power stroke. i

y it is another feature of this inventionthat the actuating gas acts against an effective area equal to the geometrical cross-sectional area of I the upper endof the hammer. The air in chamber B acts against an effective areathat is equal to the cross-sectional area of the hammer less the cross-sectional area of blind hole35. So that air pressure can act against this latter area also to helpmove the hammer downward, grooves42a-{and 42b extend downwardly and intersect lateral passageways 43a, only one of which is shown as explained above, which connect the grooves to the lower end of blind'hole 35 belowvalve member 26, as-shown in FIGS. 1A and 2A. Thus the air from valve member, 26,

flows upwardly into chamber B to act against the annular upper end of hammer 20 and also downwardly into the lower end of opening 35 to exert its pressure on the bottom of opening 35, thereby providing the maximum downward force to the hammer available for a hammer v of a given diameter and. air of a given pressure.

Means areprovided to exhaust the actuating fluid from both chambers A and B after theair therein has expanded to move the hammer in its return stroke and its power stroke, respectively, and after thesupply to v the respective chambers has been cut off. In the embodiment shown, the lower or first chamber A is ex in sleeve valve 22, through central opening 23" of the anvil into central bore 45 of bit 15, and out through the ports in the bit. To exhaust upper or second chamber B, the internal bore of housing portion is provided with groove 46. The groove is positioned to connect passageways 42a and 42b with inclined holes 47a and 47b when the hammer is a given distance below sub 12. The inclined holes connect the groove to central exhaust opening 24 in the lower part of the hammer, from where the air flows the same exhaust route as the air from chamber B.

Thus, in operation, the tool is run to the bottom of the hole and the desired weight placed on the bit. The hammer is then resting on the anvil. Chamber A is connected to openings or outlet ports 37 in the hollow valve member 26 by passageways 38 and 39ab and enlarged diameter section 35a of blind hole or opening 35, as shown in FIGS. 1A and 1B. Air under pressure is supplied to the drill pipe and to hollow valve member 26 and, in turn, to chamber A. The hammer is moved upwardly by the air pressure.

As the hammer moves up, enlarged section 35a of blind hole 35 moves away from openings 37 to cut off supply of air to the lower chamber. Hole 35 has a diameter (except for the sections of increased diameter) such that the clearance between the hole and hollow valve member 26 is small so that when openings 37 are out of register with enlarged portion 350, the flow of air to chamber A is effectively cut off. As the hammer continues upward, the lower end of the hammer clears valve sleeve 22 and a chamber A is exhausted. As the hammer continues upwardly in its over-travel, enlarged diameter section 40 of hole 35 is moved to a position to communicate with openings 36 in the valve member, as shown in FIGS. 2A and 2B. Air can now flow to chamber B and the lower end of blind hole 35 and start the hammer on its downward or power stroke toward the anvil. As the hammer moves down, enlarged diameter section 40 of hole 35 is moved away from openings 36 in the valve member and the flow of air to chamber B will stop. At that-time, or shortly thereafter, passageways 42a and 42b will be connected to annular groove 46 and the air in chamber B will be exhausted. The hammer will continue downward until it strikes the anvil which transmits the energy of the downward traveling hammer to the drill bit. Then the cycle is repeated automatically.

To shorten the over-travel of thehammer, and to accelerate it during the initial portion of its downstroke, a third chamber C is located at the upper end of chamber B. This chamber is formed by a downwardly facing bore 50 in the lower end of sub 12 that receives upper end 51 of the hammer. Upper end 51 of the hammer has a reduced diameter such that it will engage seal ring 52 in bore 50 and trap air in chamber C. The trapped air will becompressed by the upwardly traveling hammer and act as a cushion to absorb the kinetic energy of the hammer and stop its upward travel. The air that is compressed in chamber C will then start the hammer on its return trip toward the anvil.

To stop the hammer from beating on the anvil, it is only necessary to pick the drill string up and lift bit from the bottom of the hole. When this occurs, anvil 14 will move downwardly to the extent allowed by annular ring 17. This movement will result in valve member 26 being moved upwardly away from the anvil far enough that any upward travel of the hammer is not enough to align annular groove 40 with outlet port 36. Therefore the hammer is never powered into a power stroke. Preferably, annular groove 35a will be made long enough that it will remain in communication with openings 37 while the tool is suspended off bottom. The resulting flow of air to the lower chamber A will cause the hammer to hover above the anvil with the lower exhaust valve open sufficiently to accommodate the exhaust of air flowing through the tool.

In FIGS. 5-10, there is shown an impact tool which not only has the characteristics of that shown in FIGS. l-4 but also some additional ones. Therefore, like parts shown in FIGS. 5-10 have been given the same numerals as those in FIGS. 1-4 except that the numeral 1 has been added as a prefix.

In the FIG. 5-10 arrangement, not only does the actuating gas act over the total geometrical crosssectional area of the hammer during the power stroke but also across the total geometrical cross-sectional area of the hammer during the push-up stroke. Thus the lower valve member 150 extends upwardly from the anvil to have a sliding fit in counterbore 151 in the hammer. The valve member has a solid head portion 150a which acts as a piston in the counterbore. Then by providing a pressurizing passageway 152.as shown, the upper end of counterbore 151 is in fluid communication, in effect, with chamber A. Then when chamber A is alternately pressurized and exhausted, the upper end of counterbore 151 will likewise be alternately pressurized and exhausted. Thus, it can beseen that the effective area exposed to actuating gas is not only the annular area at the bottom of the hammer but also the cross-sectional area of counterbore 151.

' Moreover, the lower valve member 150 can be fitted relatively loosely in its counterbore in the anvil so that the valve member is self-aligning in the hammer counterbore in which it reciprocates. The valve member cannot be dislodged from the anvil because of the pressure acting on top of it to urge it downwardly while chamber A is pressurized. I

In this embodiment, the exhaust passages 47a of FIGS. l-4 have been replaced by a vertical groove 153, a radial groove 154 and a circumferential groove 154a, all in the hammer. Thus, the exhaust gas from the upper chamber B flows down through the housing groove 1 46, and the hammer grooves 153, 154, and 154a into counterbore15 1 from which it exhausts to the exterior of the tool via slots l50b in the lower valve member and anvil bore 123. I

The arrangement of passageways and outlet ports 36, 37,38 and 41 of FIGS. l-4 has been modified in FIGS; 5-10. Thus ports 136 and 137 are formed of bores 136a and 137a (FIG. 7) extendingthrough the wall of the hollow valve member 126 into annular grooves l36b and l37b. Also passageways 138 and 141b have been made as a relatively vertically narrow but laterally wide slots (as indicated inFIG. 9 at 138C forpassageway 138) which cooperates with the respective annular grooves 136b and 137b to provide relatively large flow areas with a minimum of travel of the hammer. Also, a small microfeed groove is cut into the bottom of slots (as indicated at 138d for passageway 138) and in the top of the slot for passageway 141b. It will be understood that thus formed passageways 138 and 141b are all of the same cross-sectional configurationexcept that the micro-feed groove is at the bottom of passageways 138 and at the top of passageways l41b. With this construction, there can be a small amount of initial feeding of actuating gas into chamber A before the hammer strikes the anvil and after chamber A is closed to exhaust. This pre-charging is not enough to cause objectionable Cushioning of the hammer blow but is enough to shorten the time required to move the hammer through its push-up stroke. Similarly the microfeed groove for passageway 141b pre-loads the hammer during the initial part of its over-travel to reduce the time required to reverse the hammers direction of movement and cause it to move through its power stroke.

Thesplined connection between the anvil and housing differs somewhat in FIGS. -10 from that of FIGS. 1-4. Thus a split nut 155 is provided which has an upper shoulder 155a providing a stop for shoulder 114a on the anvil when the tool is suspended off bottom as shown in FIG. 11. To provide a splined driving connection between the housing and anvil, the split nut has internal grooves to receive about one-half of the crosssection of rods 156. The other half of the rods reside in grooves in the anvil which are long enough that the tops of the anvil grooves do not abut the rods when the tool is suspended off bottom.

The sequence of operation for this embodiment is generally the same as that for the embodiment of FIGS. l-4. Thus, beginning with the hammer on the anvil as in FIG. 5, air passes to lower chamber A to move the hammer upwardly through its push-up stroke which is defined as terminating when the hammer has moved upwardly to open the lower valve to begin to exhaust chamber-A. However, due to inertia, the hammer continues upwardly through itsfover-travel. Justprior to the opening of the lower'valve, exhaust passage 146 will be closed off by the hammer movement from communication with upper chamber A. Shortly thereafter, air is supplied to the upper chamber B to begin to arrest the upward overtravel of the hammer and then to power it in its power stroke- While the .hammer'is travelling downwardly and before it strikes the anvil, the

upperchamber B is opened to exhaust. Also prior to the hammer striking the anvil, the chamber A is closed to exhaust and also opened to receive actuating air to move the hammer in its return stroke after it has struck the anvil. However, this is timed so that enough air does not flow into chamber A to seriously cushion the flow of the hammer on the anvil- A check valve 160 canbe provided at the upper end of the tool such as in sub 112 to prevent back flow of fluids such as water in the hole into the drill pipe while the tool is being lowered into or raised out of the hole. An improved check valve is shown in FIG. 12. Thus the check valve has an outer. body 161 closed at its lower end andsupported in the tool by a'support ring 162 resting on a shoulder in sub-112. A resilient ring 163 is placed betweenthe 'lowerend of pipe section 164 to hold the support ring in place while permitting variacheck valve. This movement causes passageways 169 i to move out of register with ports 168 thereby effectively trapping air under pressure in the check valve to hold it closed. However, when air flow resumes, it will build in pressure to act to open the check valve which again opens ports 168 to the interior 170 so that the pressure therein is equalized with the exterior pressure after which the valve remains open by gravity. By positioning ports, 168 intermediate the length of the outer valve body 161 and by extending passageways 169 downwardly to open into the interior'170 adjacent the bottom of the outer body, any liquid in the interior will tend to be expelled through these passages to the exterior of the check valve each time the same moves to closed position.

Y From the foregoing description of one embodiment of this invention by way of example, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with the interior 170 of the check valve will be pressurized v to a pressure equal to that exteriorly of the check valve.

other advantages which are obvious and which are inherent to the apparatus.

The invention having been described, what is claimed l. A gas powered impact tool comprising: a housing adapted to be connected to a source of gas under pressure, an anvil located in the lower end of the housing, a hammer located in the housing to reciprocate therein and strike the anvil at the ends'of its power strokes, a stationary valve member connected to the housing and in telescoping relationship with the hammer, said stationary valve member having outlet port means to which gas under pressure is supplied from the source of gas when the housing is connected thereto, first and second passageway means in the hammer to conduct the gas to act against the lower and upper end surfaces of the hammer, respectively, to cause the hammer to reciprocate, each passageway means having an inlet port located in said portion of the hammer thatis in telescoping relationship with the stationary valve memher to register with the outlet port means of the stationary valve member to conduct the gas to act against the lower and upper end surfaces alternately as the hammer reciprocates, and means for exhausting the gas from the housing after the gas has acted against the lower and upper surfaces of the hammer including a first exhaust passageway in the hammer extending upwardly from the lower end of the hammer part way through the hammerand having an inletv port on the side of the hammer,a second exhaust passageway extending from the upper end of the hammer to an exhaust port in the side of the hammer, and an internal groove in the housing connecting the inlet and outlet ports of the first and second exhaust passageways to exhaust the gas from the upper chamber when the hammer has moved a predetermined distance from the upper end of the housing. I 2. The impact tool of claim 1 in which the upper portion of the hammer includes an opening in the hammer and wherein the stationary valve member is an elongated hollow member located in the upper end of the housing and extending into the opening in'the hammer to provide the telescoping relationship therewith.

3. The impact tool of claim 2 in which the opening extends only partly through the hammer and the second passageway means also conducts gas under pressure to the opening in the hammer between the bottom of such opening and the stationary valve member when the second passageway means is conducting gas to act against the upper end surface of the hammer to allow the pressure of the gas to act against an area equivalent to the entire cross-sectional area of the upper end of the hammer.

4. A gas powered impact tool for connecting into a drill string above a drill bit, comprising: tubular housing adapted to be connected into the drill string; a hammer located in the housing for longitudinal reciprocation relative thereto, the hammer having an upwardly opening blind hole in its upper end; anvil means positioned at one end of the housing including an-anvil face to be struck by the hammer and to transmit the impact of the hammer to a drill bit; and means for directing actuating gas to act against the ends of the hammer alternately to cause the hammer to reciprocate in the housing, said means including lower and upper chambers in the housing in fluid communication respectively with the lower and upper ends of the hammer, a closed end, hollow member extending into the housing through the upper end thereof and into the blind hole in the upper end of the hammer, said hollow member being in fluid communication with the drill string when the impact tool is connected therein'to be charged with gas under pressure from the drill string, valve means for alternately charging the chambers with gas from the hollow member to cause the hammer to reciprocate in the housing and strike the anvil means during each reciprocation, said valve means including outlet port means in the hollow member through which gas therein can flow, first passagewaymeans in the hammer connected to the lower chamber and positioned on the hammer to be connected to the outlet port means on the hollow member when the hammer has moved a predetermined distance through its power stroke to allow gas to flow from the hollow member to the lower chamber and move the hammer in a return stroke after the hammer has struck the anvil face, second passageway means in the hammer connected to the upper chamber and positioned on the hammer to be connected to the outlet port means on the hollow member when the hammer is a predetermined distance from the upper end of the housing to allow gas to flow from the hollow member to the upper chamber and move the hammer in a power stroke toward the anvil face,'and means for alternately exhausting the two chambers when the hammer has traveled predetermined distances from the anvil means and the upper end of the housing, respectively, including means for exhausting the gas from. the upper chamber comprising-a first exhaust passageway in the hammer extending upwardly from the end of the hammer adjacent the anvil face part way through the hammer and having an inlet port on the side of the hammer, a second exhaust passageway extending from the upper chamber to an exhaust port in the side of the hammer,

and an internal groove in the housing connecting the inlet and outlet ports of the first and second exhaust passageways to exhaust the gas from the upper cham-- 10 anvil located in the lower end of the housing; a hammer located in the housing for reciprocation longitudinally of the housing; and means for reciprocating the hammer to cause the hammer to impart a series of blows to the anvil, said means including a hollow member located in the upper end of the housing in fluid communication with the drill pipe to receive a supply of gas under pressure from the drill pipe and having laterally opening outlet port means through which the gas in the hollow member can flow, said hollow member having a closed end, a blind opening in the upper end of the hammer into which the hollow member extends as the hammer reciprocates, first passageway means in the hammer located to connect the outlet port means'of the hollow member to expose the lower end of the hammer to gas under pressure from the hollow member when the hammer has moved a predetermined distance through its power stroke to urge the hammer upwardly in its return stroke after the hammer has struck the anvil, said housing including a closing member located at its upper end so that the housing and the hollow member provides a chamber above the upper end of the hammer, second passagewaymeans in the hammer located to connect the outlet port means of the hollow chamber with the exhaust port when the hammer has,

moved a predetermined distance through its power stroke to discharge the pressurized gas from the chamber into the exhaust port, said anvil having an opening therein in fluid communication with the exterior of the tool and with the exhaust port of the hammer to conduct the gas discharged from the chamber'to the exterior of the tool.

6. The impact tool of claim 5 in which the second passageway means further connects the outlet port means of the hollow member with the space between the closed end of the hollow member and the bottom of the opening into which the hollow member extends so the actuating gas acts against the entire upwardly facing cross-sectional area of the hammer.

7. The impact tool of claim 5 in which the outlet port means of the hollow member includes two longitudinally spaced openings in the hollow member.

8. A gas powered impact tool comprising: a housing adapted to be connected to a source of gas under pressure; an anvil located in the lower portionof the housing; a hammer in the housing to reciprocatetherein to deliver blows to the anvil and having upper and lower counterbores into the top and bottom thereof respectively; an upper hollow valve member carried by the housing to telescope with a sliding fit into said upper counterbore and having outlet port means therethrough to which gas under pressure is applied through hte interior of the upper valve member from a gas source when the housing is connected thereto; first and second passageway meansin the hammer to conduct gas to act against the lower and upper end surfaces of the hammer, respectively, to cause the hammer to reciprocate, each passageway means having an inlet port opening into the upper counterbore and each being located to be in fluid communication with the outlet port means of the upper valve member to conduct gas to act against the upper and lower end surfaces alternately as the hammer reciprocates; a lower hollow valve member carried by the anvil to telescope with a sliding fit into the lower counterbore and having an exhaust port intermediate its ends and located so that the lower valve member restrains flow of gas from beneath the hammer as the latter moves through a portion of its return stroke and thereafter permits flow from beneath the hammer to the exterior of the tool, a pressurizing passageway providing communication between the upper end of the lower counterbore and said first passageway means sothat the effective push-up area of the hammer is the total geometrical cross-sectional area of the hammer at its lower end; and means for exhausting gas from above the hammer to the exterior of the housing when the hammer has moved through a predetermined distance through its power stroke.

9. The impact tool of claim 8 wherein the means for exhausting gas from above the hammer includes a first exhaust passageway in the hammer extending to communicate the lower counterbore adjacent the exhaust port in the lower valve member with an inlet port on a side of the hammer, and an internal groove in the housing placing the inlet port of the first exhaust passageway in fluid communication with the second passageway means to exhaust the gas from above the hammer when it has movedthrough at least a portion of its power stroke.

10. The impact tool of claim 9 wherein the second passageway means also conducts gas under pressure to the upper counterbore to pressurize its lower end when the second passageway means is conducting gas to act against the upper end of the hammer so that the effective push-down area of the hammer is the total geometrical cross-sectional area of the hammer at its upper ends.

11. The impact tool of claim 10 wherein the effective push-up and push-down areas are equal. 

1. A gas powered impact tool comprising: a housing adapted to be connected to a source of gas under pressure, an anvil located in the lower end of the housing, a hammer located in the housing to reciprocate therein and strike the anvil at the ends of its power strokes, a stationary valve member connected to the housing and in telescoping relationship with the hammer, said stationary valve member having outlet port means to which gas under pressure is supplied from the source of gas when the housing is connected thereto, first and second passageway means in the hammer to conduct the gas to act against the lower and upper end surfaces of the hammer, respectively, to cause the hammer to reciprocate, each passageway means having an inlet port located in said portion of the hammer that is in telescoping relationship with the stationary valve member to register with the outlet port means of the stationary valve member to conduct the gas to act against the lower and upper end surfaces alternately as the hammer reciprocates, and means fOr exhausting the gas from the housing after the gas has acted against the lower and upper surfaces of the hammer including a first exhaust passageway in the hammer extending upwardly from the lower end of the hammer part way through the hammer and having an inlet port on the side of the hammer, a second exhaust passageway extending from the upper end of the hammer to an exhaust port in the side of the hammer, and an internal groove in the housing connecting the inlet and outlet ports of the first and second exhaust passageways to exhaust the gas from the upper chamber when the hammer has moved a predetermined distance from the upper end of the housing.
 2. The impact tool of claim 1 in which the upper portion of the hammer includes an opening in the hammer and wherein the stationary valve member is an elongated hollow member located in the upper end of the housing and extending into the opening in the hammer to provide the telescoping relationship therewith.
 3. The impact tool of claim 2 in which the opening extends only partly through the hammer and the second passageway means also conducts gas under pressure to the opening in the hammer between the bottom of such opening and the stationary valve member when the second passageway means is conducting gas to act against the upper end surface of the hammer to allow the pressure of the gas to act against an area equivalent to the entire cross-sectional area of the upper end of the hammer.
 4. A gas powered impact tool for connecting into a drill string above a drill bit, comprising: tubular housing adapted to be connected into the drill string; a hammer located in the housing for longitudinal reciprocation relative thereto, the hammer having an upwardly opening blind hole in its upper end; anvil means positioned at one end of the housing including an anvil face to be struck by the hammer and to transmit the impact of the hammer to a drill bit; and means for directing actuating gas to act against the ends of the hammer alternately to cause the hammer to reciprocate in the housing, said means including lower and upper chambers in the housing in fluid communication respectively with the lower and upper ends of the hammer, a closed end, hollow member extending into the housing through the upper end thereof and into the blind hole in the upper end of the hammer, said hollow member being in fluid communication with the drill string when the impact tool is connected therein to be charged with gas under pressure from the drill string, valve means for alternately charging the chambers with gas from the hollow member to cause the hammer to reciprocate in the housing and strike the anvil means during each reciprocation, said valve means including outlet port means in the hollow member through which gas therein can flow, first passageway means in the hammer connected to the lower chamber and positioned on the hammer to be connected to the outlet port means on the hollow member when the hammer has moved a predetermined distance through its power stroke to allow gas to flow from the hollow member to the lower chamber and move the hammer in a return stroke after the hammer has struck the anvil face, second passageway means in the hammer connected to the upper chamber and positioned on the hammer to be connected to the outlet port means on the hollow member when the hammer is a predetermined distance from the upper end of the housing to allow gas to flow from the hollow member to the upper chamber and move the hammer in a power stroke toward the anvil face, and means for alternately exhausting the two chambers when the hammer has traveled predetermined distances from the anvil means and the upper end of the housing, respectively, including means for exhausting the gas from the upper chamber comprising a first exhaust passageway in the hammer extending upwardly from the end of the hammer adjacent the anvil face part way through the hammer and having an inlet port on the side of the hammer, a second exhaust passageway extending frOm the upper chamber to an exhaust port in the side of the hammer, and an internal groove in the housing connecting the inlet and outlet ports of the first and second exhaust passageways to exhaust the gas from the upper chamber when the hammer has moved a predetermined distance from the upper end of the housing.
 5. A gas powered impact tool comprising: a tubular housing adapted to be connected into a drill string; an anvil located in the lower end of the housing; a hammer located in the housing for reciprocation longitudinally of the housing; and means for reciprocating the hammer to cause the hammer to impart a series of blows to the anvil, said means including a hollow member located in the upper end of the housing in fluid communication with the drill pipe to receive a supply of gas under pressure from the drill pipe and having laterally opening outlet port means through which the gas in the hollow member can flow, said hollow member having a closed end, a blind opening in the upper end of the hammer into which the hollow member extends as the hammer reciprocates, first passageway means in the hammer located to connect the outlet port means of the hollow member to expose the lower end of the hammer to gas under pressure from the hollow member when the hammer has moved a predetermined distance through its power stroke to urge the hammer upwardly in its return stroke after the hammer has struck the anvil, said housing including a closing member located at its upper end so that the housing and the hollow member provides a chamber above the upper end of the hammer, second passageway means in the hammer located to connect the outlet port means of the hollow member to the chamber when the hammer is within a predetermined distance of the closing member to charge the chamber with pressurized gas from the hollow member to urge the hammer downwardly toward the anvil, an exhaust port in the hammer, and an internal annular groove in the housing for connecting the chamber with the exhaust port when the hammer has moved a predetermined distance through its power stroke to discharge the pressurized gas from the chamber into the exhaust port, said anvil having an opening therein in fluid communication with the exterior of the tool and with the exhaust port of the hammer to conduct the gas discharged from the chamber to the exterior of the tool.
 6. The impact tool of claim 5 in which the second passageway means further connects the outlet port means of the hollow member with the space between the closed end of the hollow member and the bottom of the opening into which the hollow member extends so the actuating gas acts against the entire upwardly facing cross-sectional area of the hammer.
 7. The impact tool of claim 5 in which the outlet port means of the hollow member includes two longitudinally spaced openings in the hollow member.
 8. A gas powered impact tool comprising: a housing adapted to be connected to a source of gas under pressure; an anvil located in the lower portion of the housing; a hammer in the housing to reciprocate therein to deliver blows to the anvil and having upper and lower counterbores into the top and bottom thereof respectively; an upper hollow valve member carried by the housing to telescope with a sliding fit into said upper counterbore and having outlet port means therethrough to which gas under pressure is applied through hte interior of the upper valve member from a gas source when the housing is connected thereto; first and second passageway means in the hammer to conduct gas to act against the lower and upper end surfaces of the hammer, respectively, to cause the hammer to reciprocate, each passageway means having an inlet port opening into the upper counterbore and each being located to be in fluid communication with the outlet port means of the upper valve member to conduct gas to act against the upper and lower end surfaces alternately as the hammer reciprocates; a lower hollow valve member carried by the anvil to telescope with a slIding fit into the lower counterbore and having an exhaust port intermediate its ends and located so that the lower valve member restrains flow of gas from beneath the hammer as the latter moves through a portion of its return stroke and thereafter permits flow from beneath the hammer to the exterior of the tool, a pressurizing passageway providing communication between the upper end of the lower counterbore and said first passageway means so that the effective push-up area of the hammer is the total geometrical cross-sectional area of the hammer at its lower end; and means for exhausting gas from above the hammer to the exterior of the housing when the hammer has moved through a predetermined distance through its power stroke.
 9. The impact tool of claim 8 wherein the means for exhausting gas from above the hammer includes a first exhaust passageway in the hammer extending to communicate the lower counterbore adjacent the exhaust port in the lower valve member with an inlet port on a side of the hammer, and an internal groove in the housing placing the inlet port of the first exhaust passageway in fluid communication with the second passageway means to exhaust the gas from above the hammer when it has moved through at least a portion of its power stroke.
 10. The impact tool of claim 9 wherein the second passageway means also conducts gas under pressure to the upper counterbore to pressurize its lower end when the second passageway means is conducting gas to act against the upper end of the hammer so that the effective push-down area of the hammer is the total geometrical cross-sectional area of the hammer at its upper ends.
 11. The impact tool of claim 10 wherein the effective push-up and push-down areas are equal. 